If you use the Subclipse plugin to access subversion repositories from Eclipse using the ssh+svn protocol, you may see errors like this:
when you try to do too many things at once.
When I tried switching to JavaHL instead of SVNKit, I got different errors, so that was out.
Adding this line to my eclipse.ini file fixed it though:
It prevents the SVNKit adapter from issuing multiple sessions through a persistent SSH connection, which seems to trigger the error on some SSH servers at least.